Abstract

The Southern Annular Mode (SAM) is the leading mode of atmospheric interannual variability in the Southern Hemisphere (SH) extra-tropics. Here, we assess the stationarity of SAM spatial correlations with instrumental and paleoclimate proxy data for the past millennium. The instrumental period shows that temporal non-stationarities in SAM teleconnections are not consistent across the SH land areas. This suggests that the influence of the SAM index is modulated by regional effects. However, within key-regions with good proxy data coverage (South America, Tasmania, New Zealand), teleconnections are mostly stationary over the instrumental period. Using different stationarity criteria for proxy record selection, we provide new austral summer and annual mean SAM index reconstructions over the last millennium. Our summer SAM reconstructions are very robust to changes in proxy record selection and the selection of the calibration period, particularly on the multi-decadal timescale. In contrast, the weaker performance and lower agreement in the annual mean SAM reconstructions point towards changing teleconnection patterns that may be particularly important outside the summer months. Our results clearly portend that the temporal stationarity of the proxy-climate relationships should be taken into account in the design of comprehensive regional and hemispherical climate reconstructions. The summer SAM reconstructions show no significant relationship to solar, greenhouse gas and volcanic forcing, with the exception of an extremely strong negative anomaly following the AD 1257 Samalas eruption. Furthermore, reconstructed pre-industrial summer SAM trends are very similar to trends obtained by model control simulations. We find that recent trends in the summer SAM lie outside the 5–95% range of pre-industrial natural variability.

Notes

Acknowledgements

This is a contribution to the Past Global Changes (PAGES) 2k Network. Researchers from the PAGES2k consortium are acknowledged for providing access to data and metadata information. We thank Michael N. Evans for discussions. This study was supported by the Swiss National Science Foundation (SNF) Ambizione grant PZ00P2_154802. DJK receives funding through the Australian Research Council Centre of Excellence for Climate System Science (CE110001028). MJC acknowledges CONICYT-Chile through grants PAI79160105 and FONDAP15110009. RN, MG, and CD designed the study; CD and RN led the writing and conducted the data analysis. All authors jointly discussed and contributed to the writing.